The invention relates to a combustion engine and to a method for operating an internal combustion engine.
In an internal combustion engine with an exhaust manifold which is integrated in the cylinder head, larger amounts of heat energy are stored in the exhaust manifold than in conventional internal combustion engines with an external exhaust manifold. This may lead to the coolant in the integrated exhaust manifold medium starting to boil after turning off the internal combustion engine, which would lead to damage to the coolant. Such an undesired boiling of the coolant in the region of the exhaust manifold can be avoided in that the integrated exhaust manifold is still cooled for a certain period of time by a so called shut down cooling after turning off the internal combustion engine.
However, when the shut down cooling occurs by circulating the coolant by means of an electric coolant pump through a continuous water jacket of the cylinder crankcase, the cylinder and the integrated exhaust manifold, only a relatively small portion of the circulated coolant is conducted into the exhaust manifold. In order to ensure a sufficient cooling, the electric coolant pump thus has to circulate a large amount of coolant and with this has to be dimensioned correspondingly great.
In addition, the fast warming up of internal combustion engines after the cold start will be very important in the future because this not only allows ensuring a decrease in friction after the cold start and with this a lower fuel consumption, but also a decrease of pollutant emission. In an internal combustion engine of a motor vehicle, a fast warming up also allows conducting warmed-up coolant to the heater heat exchanger of the motor vehicle in order to heat the interior of the motor vehicle for increasing the comfort of the passengers, However, a fast heating up of the internal combustion engine requires that the coolant in the water jacket of the internal combustion engine is not or hardly moved immediately after its star. This in turn is only possible until the coolant, at the sites where it heats up the fastest, almost reaches its boiling point. In internal combustion engines with integrated exhaust manifold, one of these sites is located in the integrated exhaust manifold. When a boiling of the coolant is to be prevented in this location by circulating the coolant through the water jacket, similar problems arise as previously described for the shut down cooling. This means, only a relatively small amount of the circulated coolant reaches the integrated exhaust manifold while a relatively large amount of the coolant circulates through the cylinder crankcase. As a result, the cylinders are unnecessarily cooled there so that at least the desired lowering of the friction and the fuel consumption cannot be achieved.